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Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Internal energy is the only factor controlling the extent of rDA reactions, and temperature is usually the only variable cited for these reactions. Thus, there are no conditions which can be regarded as "typical." For rDA reactions that afford a volatile product, removal of this product may facilitate the reaction, although most of these reactions (nitrogen- and oxygen-releasing rDA, for instance) are irreversible without any extra inducement.

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Supplementary materials include NMR and MS-data of compounds 5b-5f and 2b-2f.

Highly substituted phthalides including a key intermediate in the synthesis of mycophenolic acid were prepared by the Diels-Alder reaction of 3-(phenylthio- or 3-(phenylsulfinyl)-2-(5H)-furanones with silyloxydienes.

Author's Organization:Faculty of Pharmaceutical Sciences:Nagasaki University, Faculty of Pharmaceutical Sciences:Nagasaki University, Faculty of Pharmaceutical Sciences:Nagasaki University, Faculty of Liberal Arts:Nagasaki University, Faculty of Pharmaceutical Sciences:Nagasaki University

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Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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We gratefully acknowledge the financial support of this work by INDUNIV and RCMI Grant #G12RR03051. We also thank Bristol-Myers-Squibb, Humacao and the University of Puerto Rico at Humacao for use of their NMR facilities.

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With an optimized imidate directing group identified for additions to aliphatic aldehyde 2c, a range of different aldehydes 2 was surveyed (). This transformation was found to be very general with linear and sterically hindered aldehydes providing phthalides in good yields (6t and 6s, respectively). Moreover, oxygen functionality could be placed at the α-position of the aldehyde to provide sites for additional synthetic transformations. Both N-methoxy benzimidate (3a) and N-3,5-bistrifluoromethylphenyl benzimidate (10a) were evaluated for each of the aliphatic aldehydes with benzimidate 10a providing higher yields for almost all of the aldehydes examined. The only exception was α-benzyloxyacetaldehyde for which benzimidate 3a provided phthalide 6u in a significantly higher yield.

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The Rh() catalyst used here is stable to air and water, and therefore, the feasibility of performing this novel transformation on the bench top was examined to enhance the practicality of the method (). Coupling reactions between benzimidate 3a and aldehyde 2a were carried out with set up on the bench top under an air and also under a N2 atmosphere (eqn (5)). Both reactions afforded the product 6d in comparable yields. Furthermore, these reactions proceeded in only slightly lower yield than when the reaction was set up using rigorous inert atmosphere techniques in a glovebox. The bench top reaction between 10a and the aliphatic aldehyde 2c under a N2 atmosphere was similarly successful (eqn (6)). However, a significant reduction in yield was observed when the reaction with the aliphatic aldehyde was carried out in air.

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In summary, we have developed a simple two-step procedure to synthesize benzoxazinones from phthalides via an aminolysis-Hofmann rearrangement procedure. For the difficult aminolysis of the benzolactone ring, in situ prepared aluminum amide reagents were successfully employed. For the Hofmann rearrangement, BTI was selected and was shown to be sufficiently mild to not oxidize the benzylic alcohol groups. Instead the hydroxyl group reacted with the intermediate isocyanate to form the desired six-membered ring benzoxazinones. The method can potentially be applied to available phthalide libraries.

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We next explored the possibility of extending the substrate scope to unactivated aliphatic aldehydes (). Rh()-catalyzed additions to this class of aldehydes has not previously been demonstrated even with trapping of the alcohol addition products through oxidation. Conducting the reaction with cyclohexanecarboxaldehyde (2c) under the standard conditions afforded the expected phthalide 6q in only 32% yield (entry 1). Adding 0.5 equiv. of K2CO3 to the reaction mixture in an attempt to minimize acid catalyzed aldehyde self-condensation improved the yield to 54% (entry 2). After several failed attempts to further improve the yield, we turned our attention to structural variation of the imidate directing group, in particular, by introducing an N-aryl rather than the N-methoxy substituent (entries 3–6). The electronic properties of the N-aryl substituent had a considerable impact on the reaction yield, with more electron-deficient aryl groups providing the highest yields (entries 5 and 6). The N-3,5-bistrifluoromethylphenyl benzimidate (10a) proved to be optimal and provided phthalide 6q in 67% yield (entry 6). Given the success of coupling 10a with aliphatic aldehyde 2c, we also examined its coupling to aromatic aldehyde 2a, and while phthalide product 6d was obtained in 71% yield, this was slightly lower than that observed for the corresponding N-methoxy benzimidate 3a (6d, ).

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